Electrostatic precipitator

ABSTRACT

An electrostatic precipitator for collecting acidic elements in an acid-laden gas passing therethrough comprising: a shell; a plurality of substantially flat lead plates which form collector electrodes within the shell and define gas passages between adjacent ones of the collector electrodes for collecting the acidic elements thereon; and at least one acid-resistant discharge electrode in each of the gas passage between adjacent collector electrodes for ionizing the acidic elements in the gas for causing collection of the acidic elements by the collector electrodes.

United States Patent 1191 Gibbs et al.

1451 Aug. 27, 1974 ELECTROSTATIC PRECIPITATOR [75] Inventors: Everett Ralph Gibbs, Phoenix;

William Howard Tully, Cockeysville, both of Md.

[73] Assignee: Koppers Company, Inc., Pittsburgh,

[22] Filed: May 22, 1973 [21] Appl. No.: 362,834

[58] Field of Search 55/2, 150, 151, 152, 147, 55/148, 130, 154, 156', 29/462, 505

[56] References Cited UNITED STATES PATENTS 1,541,677 6/1925 Anderson 55/130 1,604,553 10/1926 Hechenbleikne 55/154 X 2,231,330 2/1941 Gove 55/151 2,815,824 12/1957 Armstrong et al.. 55/130 2,852.093 9/1958 Streuber 55/147 X 3.248.857 5/1966 Weindel et al.. 55/118 3,529,594 11/1950 Chamberlin 55/130 3,750,373 8/1973 Olson 55/148 X FOREIGN PATENTS OR APPLICATIONS 558,171 12/1943 Great Britain 55/150 GAS LET

1,251,054 12/1960 France ..55/150 OTHER PUBLICATIONS German Printed Application No. 1,001,239, printed Jan. 24, 1957, 1 page.

German Printed Application No. 1,008,259 printed May 16, 1957, 3 pages.

Primary ExaminerDennis E. Talbert, Jr. Attorney, Agent, or FirmOlin E. Williams; Oscar B. Brumback; Boyce C. Dent ABSTRACT An electrostatic precipitator for collecting acidic elements in an acid-laden gas passing therethrough comprising: a shell; a plurality of substantially flat lead plates which form collector electrodes within the shell and define gas passages between adjacent ones of the collector electrodes for collecting the acidic elements thereon; and at least one acid-resistant discharge electrode in each of the gas passage between adjacent collector electrodes for ionizing the acidic elements in the gas for causing collection of the acidic elements by the collector electrodes.

15 Claims, 9 Drawing Figures GAS OUTLET ELECTROSTATIC PRECIPITATOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to electrode retaining or supporting means in an electrostatic pre cipitator and more specifically to a means for retarding the tendency of lead plates used as collecting electrodes in an acid-mist precipitator to creep.

2. Description of the Prior Art Electrostatic precipitators have previously been used to remove acidic elements from an acid-laden gas prior to the gas being released to the outside atmosphere. One requirement of such precipitators is assuring that all materials used within the gas treatment chamber are of an acid-resistant type. The conventional dust or particle removal electrostatic precipitator is inadequate for acid removal because the gas treatment chamber is composed of steel and other metals that are easily attacked by acid. Therefore a different type of precipitator must be used for removal of acid-elements.

Exotic metals and metallic alloys, such as, for example, titanium, tantalum, stainless steel, and nickel-base alloys can be used which are acid-resistant to replace the steel used in conventional electrostatic precipitators, but the increase in cost would be exorbitant and consequently they have not been utilized to any great extent. Lead, on the other hand, has been found to be adequately acid-resistant for use in acid-removing electrostatic precipitators and it has the added advantage of being relatively low in cost.

The acid mist precipitators in use today employ a series of vertically extending tubes which are composed of lead. These lead tubes are arranged within a shell enclosure to form the collector electrodes for the acidic elements. The lead collector tubes are secured to and supported at the top by an acid-resistant plate which is secured to the precipitator shell. The collector tubes support a lead plate near the bottom of the tubes and the lead plate is also secured to the walls of the precipitator. Suspended within each lead collector tube is a single acid-resistant discharge electrode rod, usually made of lead. The acid-laden gas enters the bottom of each lead tube and exits as a relativeclean gas at the top of each lead tube. As the acid-laden gas passes through the lead collector tube and around the discharge rod, the discharge rod ionizes the acidic elements within the gas and the acidic elements are then attracted to the lead collector electrode tube and deposited thereon. The acid then runsdown the inner surmaterial is insufficient to carry its own weight and failure results. In addition, the downward creep of the tubes creates a stress and deformation in the lower lead plate, accelerating failure of that member. When this occurs, gas and acid can escape through the tube and lower lead plate and attack the non-acid-resistant metals within the system, and escape to the atmosphere.

A second disadvantage of using tubular collector electrodes is the inefficiency of the system. All the space between adjacent tubes is not used since the acid-laden gas goes only through each tube. The unused space between the'tubes is very uneconomical from the standpoint that there is a vast unproductive area within each precipitator. This causes the size and cost of such a precipitator to increase.

A third disadvantage of using tubular collector electrodes is that the precipitator cannot have multiple electrical fields within one confine as is used with conventional dust and particle removing electrostatic precipitators. Each lead collector tube has one discharge electrode rod suspended within the collector tube, consequently only one electrical field within the length of the collector tube is possible. It does not allow a weak field at the bottom, a strong field in the middle, and a stronger field at the top in order to insure that all acidic elements are removed. Thus the tubular concept is not as efficient as the conventional electrostatic precipitator having multiple fields.

Apparently, the use of lead collector electrodes in flat plate type precipitators has not been attempted prior to the present invention because the problems of lead creep and thermal stresses appear more formidable than in the tube type precipitator. Flat plates have long, thin bottom surfaces which do not lend themselves to being supported such as do lead tubes by virtue of their circular configuration. Furthermore, tubes are less subject to warpage from stresses than are flat plates because tubular shapes are inherently selfreinforcing. The successful use of flat lead plates would provide the most efficient use of space and permit the use of multiple electrical fields, both of which are advantageous as previously explained. And, lead tubes are known to creep thereby requiring maintenance and/or replacement from time to time. Thus, the use of flat lead plates as collector electrodes would overcome the many disadvantages of tubular lead electrodes.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrostatic precipitator with a lead collector electrode that will overcome the aforementioned and other disadvantages; thus, this invention provides an electrostatic precipitator with substantially flat lead collecting electrode plates and a support frame for the plates that will effectively retard the tendency of lead to creep.

I This is generally accomplished by providing an electrostatic precipitator which is used for collecting acidic elements in an acid-laden gas passing therethrough with a shell; a plurality of substantially flat lead plates forming collector electrodes spaced within the shell and defining gas passages therebetween for collecting the acidic elements thereon; the collecting electrodes having anti-creep means for retarding creep in the lead plates; and at least one acid-resistant discharge electrode in each of the gas passages between the collector electrodes for ionizing the acidic elements in the gas for causing collection thereof by the collector electrodes.

The above and further objects and novel features of the invention will appear more fully from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings wherein like parts are marked alike:

FIG. 1 is a schematic illustration in front elevation of an electrostatic precipitator of the present invention showing the lead collector plate and framed acidresistant discharge electrode assembly suspended within the precipitator;

FIG. 2 is a schematic illustration in front elevation of an electrostatic precipitator showing the lead collector plate of FIG. 1 used in combination with a plurality of individually suspended acid-resistant wire discharge electrodes;

FIG. 3 is a schematic illustration in side elevation of the electrostatic precipitator of FIG. 1 taken along the line IIIIII and showing the gas passages between adjacent lead collector electrode plates;

FIG. 4 is a perspective view of the lead collector plates and the framed acid-resistant discharge electrodes of FIG. 1 looking downward and to the left;

FIG. 5 is a front elevation view of the lead collector plate of FIG. 1 showing the lead plate wrapped around a reinforcing frame and support holes located on the vertically extending support members;

FIG. 6 is a partial cross-sectional view of the lead collector plate of FIG. 5 taken along line VIVI showing the manner in which the lead plate is wrapped around the vertical support members;

FIG. 7 is a cross-sectional view of the lead collector plate of FIG. 5 taken along line VIIVII showing the manner in which the lead plate is wrapped around the horizontally extending top and bottom members;

FIG. 8 is a partial cross-sectional view of the lead collector plate of FIG. 5 taken along line VIlIVlIl showing the lead plate indented within the support holes in the vertical support members; and

FIG. 9 is'a flow diagram illustrating the preferred sequential method steps for removing acidic-elements from an acid-laden gas passing through an electrostatic precipitator of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1, 3, and 4, the invention generally comprises an electrostatic precipitator, denoted generally by numeral 10, for removing acidic elements from an acid-laden gas passing therethrough. Precipitator 10 comprises a shell 12; a plurality of substantially flat lead plates, denoted generally by numeral 14, (FIG. 4) forming a collector electrode assembly, denoted generally as numeral 16, (FIGS. 3 and 4) spaced within shell 12 and defining gas passages 18 (FIG. 3) between adjacent collector electrode assemblies 16 for collecting the acidic elements upon the lead plates 14; at least one acid-resistant discharge electrode, denoted generally by numeral 20, (FIGS. 1, 3, and 4) in each of the gas passages 18 between the collector electrode assemblies 16 for ionizing the acidic elements in the acidladen gas for causing collection of the acidic elements by collector electrode assemblies 16.

More specifically the present invention as shown in FIGS. 1, 3, and 4 comprisesa shell 12 which completely encloses the internal components of electrostatic precipitator 10. Shell 10 includes a gas inlet port 22 by which the acid-laden gas enters into a treatment chamber 24. The acid-laden gas is brought to the gas inlet port 22 by any conventional means, such as by acid-resistant duct work (not shown). A gas outlet port 26 is located on shell 12 opposite the wall that contains gas inlet port 22. Once the acid-laden gas has been cleaned in treatment chamber 24, the gas exits from shell 12 by gas outlet port 26 and is disposed of by any conventional means such as into a gas stack.

Shell 12 also includes a hopper 28 located at the bottom of precipitator 10. As the acidic elements are removed from the acid-laden gas, droplets of acid are formed on lead plates 14, rundown the plates 14, and drop off into hopper 28 from which the acidic elements are collected and disposed of in the conventional manner.

At the top of shell 12 is an enclosed area or penthouse 30. Housed within penthouse 30 is an insulator 32 which is used to suspend the discharge electrodes 20 within gas passages 18 (FIG. 3).

Although not shown, it should be understood that the inside surfaces of shell 12 must be acid-resistant since the acid-laden gas will contact any exposed surface within treatment chamber 24. Any conventional method may be used to insure that the walls of shell 12 are acid-resistant, such as, for example, by lining the inside walls of shell 12 with lead sheets or tile. The lead sheets may be secured to the walls by placing metal straps over the lead sheets and then riveting the metal strap to the walls. Other lead sheets are placed over each metal strap and the lead sheet covering the metal strap is burned to the lead sheet covering the wall. By this means, both the metal walls and metal straps are protected from being contacted by the acid-laden gas.

Referring again to FIGS. 1, 3, and 4, suspended within treatment chamber 24 is a plurality of acidresistant discharge electrodes 20. The discharge electrodes 20 are spaced parallel to the gas flow through the precipitator. The discharge electrodes 20 consist of a top and bottom horizontally extending metal members 34 and 36 respectively with a pair of vertically extending members 38 and 40 connected to each end of the horizontal members 34 and 36 thus forming a substantially rectangular frame, denoted generally as numeral 42 (FIGS. 1 and 4). A plurality of discharge wires 44 are horizontally spaced within frame 42 and connected to the top and bottom horizontal members 34 and 36 respectively thus forming a plurality of vertically extending discharge wires 44- within each frame 42.

To suspend each discharge electrode 20 within treatment chamber 24, a vertically extending support bar 46 is connected to the top horizontal member 34 at substantially its center. Connected to the top of support bar 46 is a horizontally extending support bar 48 (FIG. 4) which runs substantially parallel to the top horizontal member 34, and is connected to support bar 46 at substantially its center. Connected to each end of support bars 48 on each discharge electrode 20 are support channels 50 and 52 which are substantially perpendicular to each horizontal member 34 and extend substantially the width of treatment chamber 24, (FIG. 3). Preferably, support channels 50 and 52 are suspended from insulator 32 at least at two locations as shown in FIG. 3, but it should be understood that support channels 50 and 52 may be supported by one or a plurality of insulators 32. Insulators 32 are supported within penthouse 30 and electrically insulate discharge electrodes from the other metallic and electrical components of precipitator 10. Connected at one end to each insulator 32 is a vertically extending support bar 54. Support bar 54 is connected at its other end to a horizontal support bar 56 (FIG. 4) at substantially the center of support bar 56. Support 56 is connected at each end to support channels 50 and 52 in the same manner as support bars 48.

Although the above is the preferred manner in which to construct discharge electrodes 20, other types of discharge electrodes may also be used, for example, such as that which is shown in FIG. 2. The discharge electrode, denoted generally by numeral 58, is suspended from insulator 32 in the same manner as previously described. In this alternate arrangement, the support frame 42 is eliminated and only a top horizontal support member 60 is utilized. A plurality of individual vertically suspended discharge wires 62 are horizontally spaced along and connected at one end to horizontal support member 60. Connected to the other end of each discharge wire 62 is an element 64 to help keep discharge wires 62 vertically suspended within treatment chamber 24.

The frame arrangement of suspending the discharge wires is preferred overthe weight arrangement because it has been found that'discharge wires tend to oscillate within their own electrical field if the lower end of the discharge wires are not connected to a rigid support. This tendency to oscillate is undesirable because it tends to vary the field strength between adjacent collector plates and should the wire oscillate close enough to the collector plates, arcing will occur between the discharge electrode and the collector plate. Arcing is undesirable because it tends to burn a hole through the collector plate leaving the metallic reinforcing frame (to be later described) of the collector plate exposed to the acidic elements.

Since discharge electrodes 20 are suspended within treatment chamber 24, it is essential that all the components, previously described, that make up discharge electrodes 20, be resistant to or protected from attack by the acid-elements contained in the acid-laden gas. Various acid-resistant metals and metal alloys may be utilized, such as, for example lead, titanium, tantalum, stainless steel and a nickel-base alloy composed of the elements Ni, Co, Cr, Mo. Fe, Si, Mg,-V, C, P, and S which is manufactured under the tradename Hastelloy and manufactured by Stellite Division, Cabot Corp., Kokoma, Ind. The nickel-base alloy can also be identitied as ASTM B-295-64. All the mentioned elements may be used in an acid-type atmosphere, but all except lead are extremely expensive and consequently the ex-' otic type metals and metal alloys may not be practical for economic reasons. Pure lead, which is much less expensive than the exotic metals, may be used but, be cause of the problem of lead creep without adequate support, previously described, it has been found that the individual components are preferably made out of a relatively inexpensive metal such as steel covered by a layer of lead which keep the acid from contacting the metal, thus, reducing the amount of lead creep and at the same time providing a relatively efficient and economical system.

Referring to FIGS. 1, 3, and 4, suspended within treatment chamber 24 is a plurality of collector electrode assemblies 16. Each collector electrode assembly 16 is suspended between adjacent discharge electrodes 20 so that its width is parallel to the gas flow (FIG. 4) through electrostatic precipitator 10. Each collector electrode assembly 16 is substantially a solid rectangular plate thus preventing the acid-laden gas from passing through each collector electrode assembly 16, but instead the gas flow is directed between and parallel to each adjacent collector electrode assembly 16. The acid-laden gas thus flows through a gas passage 18 defined by each adjacent collector electrode assembly 16. As previously stated, suspended between adjacent collector electrode assemblies 16 and in gas passages 18 are discharge electrodes 20, previously described, thus the acid-laden gas flows by each discharge electrode 20.

The preferred manner of suspending collector electrode assemblies 16 within treatment chamber 24 is shown in FIGS. 1, 3, and 4. A plurality of U-shaped supports 66 (FIGS. 3 and 4) are secured such as by bolting or preferably by welding, to the inside gas inlet wall of treatment chamber 24. The U-shaped supports 66 are secured so they protrude into treatment cahmber 24 (FIGS. 1 and 4) and are located substantially between adjacent discharge electrodes 20 (FIG. 3). A second plurality of U-shaped supports 66 are secured to the inside gas outlet wall of treatment chamber 24 (FIG. 1) and substantially in line with the supports 66 secured to the gas inlet wall. The U-shaped supports 66 are secured high enough in treatment chamber 24 so each collector electrode assembly 16 will be properly suspended within treatment chamber v 24 in order to expose the greatest amount of surface area to the acid-laden gas.

The top rigid horizontal member 68 (FIG. 5), and to be later described, of collector electrode assembly 16 is of sufficient length to overlap the opposed U-shaped supports 66 (FIG. 1). Thus, each end of member 68 will seat within the U-shaped supports 66 as shown by the dotted lines in FIG. 1 and as shown in FIGS. 3 and 4. Thus U-shaped supports 66 provide a rigid support for each collector electrode assembly 16 and suspends the same within treatment chamber 24.

Referring now to FIG. 5, collector electrode assembly 16 generally comprises a reinforcing frame, denoted generally as numeral 70, and is shown as dotted lines in FIG. 5, and a substantially flat lead plate 14 which completely covers reinforcing frame 70 to prevent any contact between reinforcing frame 70 and the acidic elements within the acid-laden gas.

The reinforcing frame 70 includes a rigid top horizontal extending member 68 (FIGS. 5 and 7) which is of sufficient length to span substantially between adjacent inlet and outlet walls of treatment chamber 24 and to insure that the ends of member 68 will overlap and seat within the U-shaped supports 66.

A plurality of laterally spaced vertically extending support members 72, (FIGS. 5 and 6) are secured, preferably by welding, at one end to the top member 68. Vertical members 72 should be of sufficient length to extend substantially the depth of treatment chamber 24, in order to expose the maximum surface area to the acid laden gas flowing by collector electrode assembly 16.

Each vertical support member 72 has a plurality of vertically spaced apertures or holes 74, (FIGS. 5 and 8) extending into vertical support member 72. The plurality of holes 74 are preferably located on the face of member 72 that is perpendicular to the length of collector electrode assembly 16, and, in addition, are located on the face of member 72 which will have lead plate 14, to be later described, covering each hole 74. The function of holes 74 will be described in detail later.

A rigid horizontally extending bottom member 76 (FIG. and 7) which is substantially the same length as top member 68, is secured, preferably by welding, to

the lower end of each vertically extending member 72,.

thus providing a frame 70 that is substantially rectangular in shape.

The top, vertical, and bottom members 68, 72, and 76 respectively may be constructed out of many types of material, but preferably from steel. The material need not be acid-resistant because each member will be completely covered by the acid-resistant lead, to be described later. In addition, members 68, 72, and 76 may be made out of a solid bar but preferably they should be tubular in shape in order to reduce weight and, in addition, allow holes 74 to protrude through the surface of vertical member 72 (FIG. 8) and into an inner cavity 78 (FIG. 6) of member 72.

Referring to FIGS. 5, 6, 7, and 8, a substantially flat lead collecting plate 14 completely covers reinforcing frame 70 in order to keep any acidic-elements from contacting the non-acid-resistant metal that makes up reinforcing frame 70 and, in addition, primarily functions as the surface onto which the acidic-elements are collected when they are removed from the acid-laden gas by the ionizing effect produced by discharge electrodes 20.

The flat lead plate 14 is attached to and supported by reinforcing frame 70 in the following manner. Preferably, a one piece sheet of lead 80 is placed over reinforcing frame 70 on the side containing holes 74 in vertical support members 72. The sheet of lead 80 is substantially larger than reinforcing frame 70 so that it substantially overlaps top member 68, bottom member 76, and the two end vertical members 72. Lead sheet 80 is formed around each vertical member 72 (FIG. 6) so that the lead sheet 80 spanning each adjacent vertical member 72 follows substantially the centerline CL running through each vertical member 72. The overlap portions 82 of sheet 80 which overlaps each of the two end vertical members 72 are formed around each endvertical member 72 so that they overlap and contact the backside of sheet 80 forming a joint 84 thereon as shown in FIG. 6. Joint 84 is burned along its entire length in order to form an acid-impervious joint.

The top overlap portion 86 (FIG. 7) and the bottom overlap portion 88 (FIG. 7) of lead sheet 80 are likewise formed around top member 68 and bottom member 76 respectively so that they overlap and contact the backside of sheet 80 forming joints 90 and 91 respectively as shown in FIG. 7. Joints 90 and 91 are then burned along their entire length to form acidimpervious joints.

A strip of lead sheet 92 is positioned and formed around the exposed side of each of the interior vertical members 72 (FIG. 6) so that the ends 94 of sheets 92 overlap and contact the backside of lead sheet 80 forming joints 96 as shown in FIG. 6. Joints 96 are burned along their entire length in order to form an acidimpervious joint.

All the remaining intersections and joints formed by lead sheets 92 contacting lead sheet 80 and the joints formed by sheet 80 around the extending end portions of top and bottom members 68 and 76 are burned in ordear to make the entire lead plate 14 impervious to the acidic elements. thus protecting reinforcing frame from being contacted by the acidic elements.

Referring now to FIGS. 5 and 8, once lead plate 14 completely covers reinforcing frame 70, lead sheet is indented into each hole 74 in vertical members 72 to form dimples 98 (FIG. 8). By indenting lead sheet 80 into each hole 74, surface 100 of sheet 80 will contact and be supported by surface 102 of hole 74. By providing a plurality of holes 74 and dimples 98, a plurality of support points are formed over the entire surface of lead sheet 80. A spacing of about 12 inches will provide ample support. This additional support for lead sheet 80 will effectively retard the creeping characteristic inherent in lead by reducing the effect of heat and gravitational stresses that are continuallly acting upon the lead plate 14 when collector electrode assembly 16 is suspended within treatment chamber 24.

The method of collecting acidic elements in an acidladen gas is generally illustrated in FIG. 9 comprising the steps of first, passing an acid-laden gas through a collection zone; second, ionizing the acidic elements within the acid-laden gas as the gas passes through the collection zone, third, collecting the ionized acidic elements on a substantially planar leaded collection surface adjacent the collection zone; and fourth, removing the collected acidic elements from the collecting surfaces. The collecting surface is planar except for the projections caused by the vertical support members 72.

A more specific explanation of the method of removing acidic elements from an acid-laden gas will be more fully understood from the following explanation as to the operation of the invention.

In operation and referring to FIGS. 1, .3, and 4, an acid-laden gas is directed into the electrostatic precipitator 10 by any acid-resistant conventional duct means (not shown) through gas inlet port 22 (FIG. 1). The acid-laden gas is then directed through gas passages or collection zones 18 (FIG. 3) defined by the plurality of adjacently spaced lead collector electrode assemblies or planar leaded collecting surfaces 16. The acid-laden gas thus flows between each adjacent collector electrode assembly 16 (FIG. 4) toward the gas outlet port 26. Suspended in each gas passage 18 between each adjacent collecting electrode assembly 16 is the discharge electrode 20 thus allowing the acid-laden gas to flow around each discharge wire 44. It is preferred that top member 34 of discharge electrode 20 be suspended slightly below top member 68 of collector electrode assembly l6 and bottom member 42 of discharge electrode 20 be positioned slightly-above the bottom member 76 of collector electrode assembly 16 because of the possibility of buildup or acidic elements and another material along the substantially horizontal surfaces on top and bottom members 68 and 76 respectively. Should the electrode wires 44 be suspended above top member 68 and below bottom member 76, arcing may occur between electrode wires 44 and the material build-up on top and bottom members 68 and 76 respectively. Should this arcing occur it would not only decrease the efficiency of the discharge electrode 20 but may also burn a hole through lead plate 14 allowing acidic elements to contact reinforcing frame 70.

When the acid-laden gas enters gas passages 18, discharge electrodes 20 are energized by a conventional precipitator control system which causes an electrostatic field to be created around each discharge wire 44. As the acid-laden gas flows through the electrostatic fields around discharge wires 44 the acidic elements become ionized. After ionization of the acidic elements, they are attracted to the lead collector electrode assemblies 16 and collected upon the lead collecting plate 14 forming droplets of acidic elements.

The droplets of acid are removed from collector electrode assembly 16 by running down each collector electrode assembly 16 until the acidic droplets drop off bottom member 76 and into hopper 28 where the acidic elements are disposed of outside the precipitator system.

The foregoing has presented a novel precipitator for the removal of acidic elements from an acid-laden gas. A substantially flat lead collector plate is utilized for the collection of the ionized elements. The plate is constructed so as to utilize a rigid support frame which is not itself exposed to the acid-laden gas. The inherent problem of lead creep has been substantially eliminated by indenting the lead plate into numerous apertures located on the reinforcing frame that the lead plate covers. Each indented portion of the lead plate provides additional support for the lead plate which substantially decreases the creeping effect caused by the heat and gravitational stresses acting on the lead plate.

Accordingly, the invention having been described in its best embodiment and mode of operation, that which is desired to beclaimed by letters patent is:

1. An electrostatic precipitator for collecting acidic elements in an acid-laden gas passing therethrough comprising:

a shell;

a plurality of substantially flat lead plates forming collector electrodes spaced within said shell and defining gas passages therebetween for collecting said acidic elements thereon;

said collector electrodes each including a reinforcing frame for said lead plates, at least one of said plates covering said frame to prevent contact between said acidic elements and said frame; and

at least one acid-resistant discharge electrode in each of said gas passages between said collector electrodes for ionizing said acidic elements in said gas for causing collection thereof by said collector electrodes.

2. The electrostatic precipitator of claim 1 wherein said acid-resistant discharge electrode comprises a plurality of weighted, spaced. and vertically-extending wires individually suspended within each of said gas passages.

3. The electrostatic precipitator of claim 2 wherein said wires are made from an acid-resistant metal selected from a group consisting of lead, titanium, tantalum, stainless steel, and nickel-base alloy.

4. The electrostatic precipitator of claim 2 wherein said wires comprise non-acid-resistant metal wires covered with a layer of lead.

5. The electrostatic precipitator of claim 1 wherein said discharge electrode comprises a vertically extending frame suspended within each of said gas passages having a plurality of vertically extending wires connected between top and bottom support members of said frame.

6. The electrostatic precipitator of claim 5 wherein said frame is made from anacid-resistant metal se- 5 lected from a group consisting of lead, titanium, tantalum, stainless steel, and nickel-base alloy.

7. The electrostatic precipitator of claim 5 wherein said wires are made from an acid-resistant metal selected from a group consisting of lead, titanium, tantalum, stainless steel, and nickel-base alloy.

8. The electrostatic precipitator of claim 5 wherein said frame comprises a non-acid-resistant metal covered with a layer of lead.

9. The electrostatic precipitator of claim 5 wherein said wires comprise a non-acid-resistant metal covered with a layer of lead.

10. The electrostatic precipitator of claim 1 wherein said reinforcing frame includes:

a rigid top member extending horizontally between opposite walls of said shell and supported thereon;

a portion of said plate indented into said apertures for supporting said plate on said support members,

thereby substantially retarding the tendency of said plate to creep caused by gravity and heat stresses acting on said plate.

12. The electrostatic precipitator of claim 11 wherein said support members are substantially tubular.

13. The electrostatic precipitator of claim 1 wherein said plate is formed around said frame forming an overlap with a surface of said plate, said overlap being burned to form an acid-impervious joint.

14. In an electrostatic precipitator having a shell def ning a gas chamber therein, a gas inlet for entry of acid-laden gas into said gas chamber, an outlet for exit of purified gas from said gas chamber, a plurality of spaced, vertically extending, collecting electrode plates suspended within said shell for collecting acidic elements thereon, the improvement wherein: said discharge electrodes comprise a plurality of acid-resistant discharge electrodes suspended between adjacent ones of said collecting plates for ionizing said acid-laden gas, and said collecting electrodes include anit-creep means to retard creep of substantially flat elemental lead collecting plates comprising said electrodes.

15. The collector electrode of claim 14 wherein said anti-creep means includes:

a support frame having;

a horizontally extending tubular top support member;

a plurality of vertically extending tubular support members connected at one end to said top support member each having a plurality of holes spaced along their outer periphery; and

spaced holes on said vertical support members for providing a plurality of individual support points for said collecting plate, thereby reducing the effect of gravity and heat stresses upon said plate tending to cause said lead 

2. The electrostatic precipitator of claim 1 wherein said acid-resistant discharge electrode comprises a plurality of weighted, spaced, and vertically-extending wires individually suspended within each of said gas passages.
 3. The electrostatic precipitator of claim 2 wherein said wires are made from an acid-resistant metal selected from a group consisting of lead, titanium, tantalum, stainless steel, and nickel-base alloy.
 4. The electrostatic precipitator of claim 2 wherein said wiRes comprise non-acid-resistant metal wires covered with a layer of lead.
 5. The electrostatic precipitator of claim 1 wherein said discharge electrode comprises a vertically extending frame suspended within each of said gas passages having a plurality of vertically extending wires connected between top and bottom support members of said frame.
 6. The electrostatic precipitator of claim 5 wherein said frame is made from an acid-resistant metal selected from a group consisting of lead, titanium, tantalum, stainless steel, and nickel-base alloy.
 7. The electrostatic precipitator of claim 5 wherein said wires are made from an acid-resistant metal selected from a group consisting of lead, titanium, tantalum, stainless steel, and nickel-base alloy.
 8. The electrostatic precipitator of claim 5 wherein said frame comprises a non-acid-resistant metal covered with a layer of lead.
 9. The electrostatic precipitator of claim 5 wherein said wires comprise a non-acid-resistant metal covered with a layer of lead.
 10. The electrostatic precipitator of claim 1 wherein said reinforcing frame includes: a rigid top member extending horizontally between opposite walls of said shell and supported thereon; a plurality of rigid, laterally spaced, vertically extending support members connected at their upper ends to said horizontal support member; and a horizontally extending rigid bottom member connected to the bottom ends of said vertically extending support members, thereby forming a substantially rectangular rigid reinforcing frame.
 11. The electrostatic precipitator of claim 10 wherein said reinforcing frame further includes: a plurality of apertures spaced along the outer surface of each of said support members; and a portion of said plate indented into said apertures for supporting said plate on said support members, thereby substantially retarding the tendency of said plate to creep caused by gravity and heat stresses acting on said plate.
 12. The electrostatic precipitator of claim 11 wherein said support members are substantially tubular.
 13. The electrostatic precipitator of claim 1 wherein said plate is formed around said frame forming an overlap with a surface of said plate, said overlap being burned to form an acid-impervious joint.
 14. In an electrostatic precipitator having a shell defining a gas chamber therein, a gas inlet for entry of acid-laden gas into said gas chamber, an outlet for exit of purified gas from said gas chamber, a plurality of spaced, vertically extending, collecting electrode plates suspended within said shell for collecting acidic elements thereon, the improvement wherein: said discharge electrodes comprise a plurality of acid-resistant discharge electrodes suspended between adjacent ones of said collecting plates for ionizing said acid-laden gas, and said collecting electrodes include anit-creep means to retard creep of substantially flat elemental lead collecting plates comprising said electrodes.
 15. The collector electrode of claim 14 wherein said anti-creep means includes: a support frame having; a horizontally extending tubular top support member; a plurality of vertically extending tubular support members connected at one end to said top support member each having a plurality of holes spaced along their outer periphery; and a horizontally extending tubular bottom support member connected to the other end of each of said vertical support members; said lead collecting plate formed around said support frame for collecting said acidic elements thereon without said acidic elements contacting said frame; and a portion of said plate indented within each of said spaced holes on said vertical support members for providing a plurality of individual support points for said collecting plate, thereby reducing the effect of gravity and heat stresses upon said plate tending to cause said lead plate to creep. 